1. Field of the Invention
The present invention relates to a liquid-cooled electric motor, with a motor shaft, two bearing plates which are mounted on the end faces of the motor housing and which carry on each side at least one bearing. The motor shaft is mounted rotatably in said bearings, and the motor also includes at least one rotating hydraulic pump, for example an axial-piston, vane or gear pump, the drive shaft of which is connected to the motor shaft by way of a coupling and which is driven by the electric motor. The present invention also relates to a corresponding method.
2. Discussion of Background Information
U.S. Pat. No. 5,181,837 and U.S. Pat. No. 5,320,501 disclose electric motors according to the preamble of the present invention. Both patent specifications show an electric motor which is connected on one side or on both sides to a hydraulic pump and which drives the latter. The hydraulic fluid is in this case supplied via an inlet orifice on the housing of the motor or via a bearing plate and flows through the entire housing, thus also surrounding the stator and the rotor of the electric motor, and lubricates the bearing points and the connection between motor shaft and pump shaft. In these versions, the pumps suck in the hydraulic fluid directly from the motor space.
The motor housing and the bearing plates are designed for a special type of pump, that is to say can be used only as a fixed combination of a motor with a pump.
Since the hydraulic fluid comes directly into contact with the electric motor, the latter has to satisfy special structural and electrical requirements. On the one hand, it must, of course, be designed to be electrically insulated, and, on the other hand, it must ensure the unimpeded throughflow of the hydraulic fluid, thus obviously directly increasing the outlay and costs in production terms.
Moreover, the losses of the electric motor are, of course, increased due to an appreciably higher rotational resistance, since it has to run completely in the hydraulic fluid.